1. Field of the Invention
The present invention generally relates to a bicycle derailleur. More specifically, the present invention relates to a rear bicycle derailleur that selectively guides a chain onto each of a plurality of rear sprockets axially arranged along the rotation axis of the rear hub at the rear part of a bicycle frame. The rear bicycle derailleur of the present invention can be switched between a high normal type and a low normal type without removing the derailleur from the frame.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle rear derailleur.
Bicycles, and particularly sports-type road racers and mountain bikes, are equipped with a rear derailleur that forms an external shifter. This rear derailleur comprises a base member (an example of a stationary member) that can be mounted to the rear part of the frame, a link mechanism with one end that is mounted to the base member, a movable member that is mounted to the other end of the link mechanism and is capable of relative movement with respect to the base member, a chain guide that is pivotably mounted to the link mechanism, and a biasing member that biases the movable member. The biasing member is a coil spring, for example, and is mounted inside the link mechanism. Known types of biasing members include those that bias the movable member away from the frame (see Japanese Laid-Open Patent Application H11-263283, for example), and those that bias the movable member toward the frame (see Japanese Laid-Open Patent Application 2001-18878, for example).
The rear sprocket cluster that meshes with the chain, which is guided by the rear derailleur, has the sprockets lined up in the hub axial direction such that the diameter decreases outward in the axial direction away from the frame. Therefore, with the former type of (high normal) rear derailleur, when the inner wire of the shift cable is released, the movable member is moved away from the frame by the biasing force of the biasing member, and the chain is guided one step/shift at a time to next smaller-diameter sprocket, resulting in an upshift. Conversely, when the link mechanism of the derailleur is pulled by the inner wire, the movable member moves toward the frame against the biasing force of the biasing member, and the chain is guided one step/shift at a time to the next larger-diameter sprocket, resulting in a downshift. A rear derailleur of this configuration is called a high normal type of rear derailleur. With a high-normal rear derailleur, the state in which the chain is disposed on the highest (smallest diameter) rear sprocket is the initial position in a state in which the inner wire is pulling the least amount.
With the latter type of (low normal) rear derailleur, as opposed to a high-normal type, when the inner wire of the shift cable is released, the biasing force of the biasing member moves the movable member toward the frame, and the chain is guided one step/shift at a time to the next larger-diameter sprocket, resulting in a downshift. Conversely, when the link mechanism of the derailleur is pulled by the inner wire, the movable member moves away from the frame against the biasing force of the biasing member, and the chain is guided one step at a time to a smaller-diameter sprocket, resulting in an upshift. A rear derailleur of this configuration is called a low normal type of rear derailleur. With a low-normal rear derailleur, the state in which the chain is disposed on the lowest (largest diameter) rear sprocket is the initial position in a state in which the inner wire is pulling the least amount.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved rear bicycle derailleur. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.